This invention relates to an aluminum alloy plate for printing which permits obtaining a uniform grained surface through a surface graining process suited for offset printing and excels in fatigue resistance. The invention relates also to a method for the manufacture of this aluminum alloy plate.
Generally, aluminum and aluminum alloys are light in weight, excel in workability, are hydrophilic and easy to give surface treatment. They are widely in use as offset printing plates on account of these merits. The conventional printing plates which have been commercially available include plates of thickness 0.1-0.8 mm and in conformity to JIS 1050 (Al of purity at least 99.5%), JIS 1100 (Al--0.05-0.20% Cu alloy), JIS 3003 (Al--0.05-0.20% Cu--1.0-1.5% Mn alloy), etc. Each of these plates is subjected to a surface graining process either by a mechanical process such as ball graining or brushing or by a chemical process such as chemical etching or electrolytic etching. For improvement in printing resistance, the plate is subjected to an anodic oxidation treatment as necessary. Then, a photosensitive agent is applied to the surface of the plate. After that, a printing plate having a printing image is prepared through a plate making process such as effecting an exposure and development. The printing plate prepared in this manner is attached onto a plate cylinder. Ink is applied to the printing image part in the presence of wetting water and is transferred to a rubber blanket. With the ink transferred to the rubber blanket, printing is carried out on a paper surface. Such being the usage, the aluminum or aluminum alloy printing plate must meet the following requirements:
(1) The printing plate must readily give a uniform grained surface through a surface graining treatment for uniform coating with the photosensitive agent, for increased adhesion and for ease of wetting water control during printing.
(2) The printing plate is to be attached onto a plate cylinder by bending two ends thereof and by inserting the bent ends into grooves provided in the plate cylinder. Following this, ink is applied to the printing plate. Then, the ink is transferred to a rubber blanket by pressing the printing plate against the rubber blanket. Therefore, the bent parts of the printing plate are sustaining a repetitive stress. The printing plate is thus expected to have excellent fatigue resistance for standing this repeated bending.
While the above stated aluminum plate of JIS 1050 is given a uniform grained surface through a surface graining treatment, it is inferior in fatigue resistance. The aluminum alloy plates of JIS 1100 and JIS 3003 have a sufficient degree of fatigue resistance. However, they do not give uniform grained surfaces through the surface graining treatment. More specifically stated, the aluminum alloy plate of JIS 1100 or JIS 3003 produces a fine streaky pattern called streaks in the rolling direction of the plate. Then, the surface graining treatment results in uneven shapes of pits. The uneven pits eventually result in insufficient etching parts. Therefore, the grained surface of the aluminum alloy plate thus obtained is not desirable for use as printing plate.
The present invention is directed to the solution of this problem.